Systems and methods for implementing lightweight and reliable hybrid or electric powertrains for aircraft

ABSTRACT

This invention pertains to reliable, lightweight and efficient hybrid electric powertrain and components thereof to power hybrid electric aircraft from one or more sources of electrical energy. In particular, a novel architecture is proposed for power panels that receive, condition and distribute high levels of electrical power to and from the propulsion electric motors and the one or several sources of electrical energy. Systems and methods for architecting the power panels using efficient, reusable and modular power electronics building blocks (PEBBs) is described, along with additional systems and methods for the optimal control of the power panels and components thereof. In addition, novel systems and methods are described for the efficient and lightweight thermal management for hybrid electric powertrain components, ranging from distribution manifolds for the powertrain or power panels, to micro fluid channels for cooling electronics with extreme heat flux. Additional disclosures are made pertaining to fail-safe architectures for plug-in series hybrid-to-electric powertrain, to the efficient in-ground charging of the stored electric energy sources, to the efficient control of permanent magnet generators, and to novel inverter technologies for the hybrid electric powertrain.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/780,660 entitled Systems and Methods for HybridElectric Aircraft Powertrains, filed on Dec. 17, 2018, the entiredisclosure of which is incorporated herein by reference. Thisapplication is related to U.S. patent application Ser. No. 16/107,821entitled System Controller for Series Hybrid Powertrain, filed on Aug.21, 2018, the entire disclosure of which is incorporated herein byreference.

BACKGROUND

Transportation systems and transport platforms are an important part ofthe infrastructure used to enable commerce and the movement of peoplebetween locations. As such, they are essential services for the growthof an economy and the development of a society. Over the years, severaltypes of transportation systems have been developed, each typically withtheir own focus, advantages and drawbacks.

A key challenge for transportation is the developing “gap” over regionaldistances, where much of the world is left without a high-speed mode.Competitive pressures have driven a 70-year decline of air over thesedistances. And the impact of high-speed rail is limited by economics toa few dense corridors. As a result, the last time the US travel surveywas conducted in 2001, 90 percent of all long-distance trips were overregional distances from 50 to 500 miles. Yet just 2 percent of thesewere by air, with auto at a staggering 97 percent. This has had atremendous impact on mobility and economic development. Regionaldoor-to-door mobility has stagnated: travel times by highway have notimproved for decades; and flight times have stretched given slowercruise speeds and increasingly congested airports. Meanwhile, the steadyconsolidation of air services to a declining set of major hubs has leftmany communities disconnected from the global air network, with severeimpact on their economy and ability to attract investment.

This bleak landscape is poised for dramatic change as sharing,electrification and autonomy converge to enable fast and flexibleregional transport at scale. Intra-urban travel is already beingreshaped by ridesharing, car sharing, car and van pooling. Electricvehicles and driverless technologies will take this further. Lowerfares, improved productivity and reduced congestion will dramaticallyexpand utility and extend range. Crucially, as recognized by theinventors, the transformation on the ground will take to the skies,extending impact of this “new transport” to regional, and eventually,intracontinental ranges. A new breed of small- to mid-sized hybridelectric aircraft will usher in a golden era of regional air. Frequentdepartures of smaller aircraft from a large number of smaller airfieldswill enable air travel much faster than today and at much lower fares.Over time, rapidly improving batteries will further reduce costs andextend range, while increasing acceptance of drones will graduallyreduce the need for pilots onboard, accelerating the trend.

As recognized by the inventors, this scale-out of air transport viasmall to mid-sized aircraft flying regional ranges is a direct result ofthe unique operating economics of range-optimized hybrid electricaircraft, enhanced further by future autonomy. While conventionalaircraft are particularly suited for moving large number of people overgreat distances, and do not operate efficiently over shorter (e.g.,regional) distances, at smaller sizes, and with fewer passengers. Incontrast, hybrid electric aircraft are free of the scale and rangeeconomics that plague regional aviation today. Smaller electric aircraftcan fly as efficiently as larger ones. And relatively small electricsflying regional are competitive with the largest conventional jetsflying long-haul. Released from the constraints of scale and range,operators will mold aircraft, frequency and routes to travel patterns.The air network that emerges will be distributed, with frequent flightsto a large number of community and urban airports, a contrast to theconcentrated network of today.

Embodiments described herein relate to aspects important to the arrivalof hybrid electric aviation, such as the development of reliable,lightweight and efficient hybrid electric powertrain and componentsthereof to power hybrid electric aircraft from one or more sources ofelectrical energy.

SUMMARY

The terms “invention,” “the invention,” “this invention” and “thepresent invention” as used herein are intended to refer broadly to allof the subject matter described in this document and to the claims.Statements containing these terms should be understood not to limit thesubject matter described herein or to limit the meaning or scope of theclaims. Embodiments of the invention covered by this patent are definedby the claims and not by this summary. This summary is a high-leveloverview of various aspects of the invention and introduces some of theconcepts that are further described in the Detailed Description sectionbelow. This summary is not intended to identify key, required, oressential features of the claimed subject matter, nor is it intended tobe used in isolation to determine the scope of the claimed subjectmatter. The subject matter should be understood by reference toappropriate portions of the entire specification of this patent, to anyor all drawings, and to each claim.

Briefly, this disclosure pertains to reliable, lightweight and efficienthybrid electric powertrain and components thereof to power hybridelectric aircraft from one or more sources of electrical energy. Inparticular, a novel architecture is proposed for power panels thatreceive, condition and distribute high levels of electrical power to andfrom the propulsion electric motors and the one or several sources ofelectrical energy. Systems and methods for architecting the power panels(also referred to as “power center”) using efficient, reusable andmodular power electronics building blocks (PEBBs) is described, alongwith additional systems and methods for the optimal control of the powerpanels and components thereof. In addition, novel systems and methodsare described for the efficient and lightweight thermal management forhybrid electric powertrain components, ranging from distributionmanifolds for the powertrain or power panels, to micro fluid channelsfor cooling electronics with extreme heat flux. Additional disclosuresare made pertaining to fail-safe architectures for plug-in serieshybrid-to-electric powertrain, to the efficient in-ground charging ofthe stored electric energy sources, to the efficient control ofpermanent magnet generators, and to novel inverter technologies for thehybrid electric powertrain.

Further on the PEBBs, the power center is designed to serve as thesingle point interface between the aircraft systems and the powerelectronics modules (PEBBs), which can be integral to the powertrain.PEBBs can be designed to serve a range of functions such as an inverter,converter, rectifier, or any other power electronics component. EachPEBB is designed to be a modular unit which can be removed or installedin the power center with a minimum number of blind connections and verylimited need for space to access, as is typical of aircraftinstallations. Single point, blind-blind connections to electricalpower, controls and thermal management loops housed in the power centerfacilitate installation of PEBBs in limited space. For instance, thepower center hosts one or more cooling system loops on manifoldsallowing each PEBB to be added to the coolant loop through no-drip quickconnect/disconnect blind attachments. Further details on the design ofthe power center and PEBBs are disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The skilled artisan will understand that the figures, described herein,are for illustration purposes only. It is to be understood that in someinstances various aspects of the invention may be shown exaggerated orenlarged to facilitate an understanding of the invention. In thedrawings, like reference characters generally refer to like features,functionally similar and/or structurally similar elements throughout thevarious figures. The drawings are not necessarily to scale, emphasisinstead being placed upon illustrating the principles of the teachings.The drawings are not intended to limit the scope of the presentteachings in any way.

FIG. 1 is a schematic diagram illustrating an implementation of aplug-in series hybrid-to-electric powertrain and associated controlsystem for a hybrid-to-electric aircraft of an embodiment.

FIG. 2 is a functional diagram showing an embodiment of a PEBB-basedhybrid power panel architecture of an embodiment.

FIG. 3 shows the implementation of the PEBB-based hybrid power panel andits integration with the series hybrid powertrain and secondaryelectrical system of an embodiment.

FIG. 4 is a schematic of an in-ground system to charge hybrid orelectric powertrain leveraging a dual-use DC-AC converter of anembodiment.

FIG. 5 shows interleaving between different phase groups and betweenphases in each group for an example of carrier waveforms with 3 phasegroups of an embodiment.

FIG. 6 is an illustration of a micro channel heat sink suitable fortwo-phase cooling for applications with extremely high heat fluxrequirements, according to an embodiment.

FIG. 7 is a schematic diagram illustrating an implementation of anexample computing environment.

FIG. 8 is a schematic diagram illustrating the connection points betweena Power Panel and a Power Electronic Building Block module.

Reference is made in the following detailed description to accompanyingdrawings, which form a part hereof, wherein like numerals may designatelike parts throughout that are corresponding and/or analogous. It willbe appreciated that the figures have not necessarily been drawn toscale, such as for simplicity and/or clarity of illustration. Forexample, dimensions of some aspects may be exaggerated relative toothers, one or more aspects, properties, etc. may be omitted, such asfor ease of discussion, or the like. Further, it is to be understoodthat other embodiments may be utilized. Furthermore, structural and/orother changes may be made without departing from claimed subject matter.References throughout this specification to “claimed subject matter”refer to subject matter intended to be covered by one or more claims, orany portion thereof, and are not necessarily intended to refer to acomplete claim set, to a particular combination of claim sets (e.g.,method claims, apparatus claims, etc.), or to a particular claim. Itshould also be noted that directions and/or references, for example,such as up, down, top, bottom, and so on, may be used to facilitatediscussion of drawings and are not intended to restrict application ofclaimed subject matter. Therefore, the following detailed description isnot to be taken to limit claimed subject matter and/or equivalents.

DETAILED DESCRIPTION

The subject matter of embodiments of the present invention is describedhere with specificity to meet statutory requirements, but thisdescription is not necessarily intended to limit the scope of theclaims. The claimed subject matter may be embodied in other ways, mayinclude different elements or steps, and may be used in conjunction withother existing or future technologies. This description should not beinterpreted as implying any particular order or arrangement among orbetween various steps or elements except when the order of individualsteps or arrangement of elements is explicitly described.

Embodiments of the invention will be described more fully hereinafterwith reference to the accompanying drawings, which form a part hereof,and which show, by way of illustration, exemplary embodiments by whichthe invention may be practiced. This invention may, however, be embodiedin many different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will satisfy the statutory requirements and conveythe scope of the invention to those skilled in the art.

Among other things, embodiments described herein can relate to a system,as one or more methods, as one or more elements of an aircraft ortransportation system, as one or more elements or functional modules ofregional aircraft transportation system, or as one or more devices.Embodiments can include a hardware implemented embodiment, a softwareimplemented embodiment, or an embodiment combining software and hardwareaspects. For example, in some embodiments, one or more of theoperations, functions, processes, or methods described herein for use inthe flight control (or other form of control) of an aircraft or of atransportation system may be implemented by one or more suitableprocessing elements (such as a processor, microprocessor, CPU,controller, etc.) that is part of a client device, server, or other formof computing or data processing device/platform and that is programmedwith a set of executable instructions (e.g., software instructions),where the instructions may be stored in a suitable data storage element.In some embodiments, one or more of the operations, functions,processes, or methods described herein may be implemented by aspecialized form of hardware, such as a programmable gate array,

Following below are more detailed descriptions of various conceptsrelated to, and embodiments of, inventive methods, apparatus and systemsfor facilitating implementation of a powertrain for hybrid electricaircraft. It should be appreciated that various concepts introducedabove and discussed in greater detail below may be implemented in any ofnumerous ways, as the disclosed concepts are not limited to anyparticular manner of implementation. Examples of specificimplementations and applications are provided primarily for illustrativepurposes.

Fail-Safe Hybrid Electric Powertrain and Secondary Electrical Systems

A hybrid electric aircraft is typically a type of an aircraft that mayintegrate and/or combine one or more stored electrical energy sources(e.g., batteries, supercapacitors, etc.) with one or more generatedelectrical energy sources (e.g., turbine-driven generators, fuel cells,etc.). A hybrid electric aircraft may employ a propulsion powertrain,such as a series hybrid powertrain, for example, as a source ofpropulsive power. In this context, “series hybrid powertrain” refers toa system of components or elements capable of generating, receiving,conditioning, and/or distributing electrical power from one or moreelectrical energy sources in order to drive or operate a particularelectrical machine that provides mechanical power for an associatedpropulsion system.

As will be seen, electrical energy sources may comprise, for example,generated electrical energy sources and stored electrical energysources. To illustrate, depending on an implementation, generatedelectrical energy sources may comprise, for example, electricalgenerators driven by turbines or powered by fuel cells, and storedelectrical energy sources may comprise, for example, batteries orsupercapacitors. Thus, depending on a particular power demand, which maybe based, at least in part, on specific sections of a flight (e.g.,takeoff, cruise, landing, etc.), a particular electrical energy sourcemay provide a primary electromotive force, for example, and, in someinstances, other electrical energy source may augment the primary sourcein a suitable manner, such as implemented via a so-called “power split”that determines the fraction of power delivered by each source.

In the following, we refer to a hybrid-to-electric aircraft or thehybrid-to-electric powertrain, which integrate and/or combine one ormore stored electrical energy sources, with optionally one or moregenerated electrical energy sources. This enables the aircraft orpowertrain to be offered with (hybrid electric) or without (electric)the optional generated electrical anergy sources installed. Further,this enables the optional generated electrical energy sources to beremoved if installed previously such that the platform goes from hybridelectric to electric, or to be added-on if not installed previously,such that the platform goes from electric to hybrid electric. Such adesign provides flexibility to accommodate the rapid development ofelectrical energy sources over the operating life of these platforms,and the wide range of applications anticipated. Aircraft and powertrainwith generated electrical energy sources installed (hybrid electric) areready for the transition to electric once technologies of the storedelectrical energy sources improve sufficiently. Alternately, aircraftand powertrain on operations with appropriately short ranges could forgothe generated electrical energy sources altogether, when the storedelectric energy sources are sufficient for these.

Furthermore, in the following, we refer to a “plug-in hybrid” or“plug-in hybrid-to-electric” powertrain as one where the storedelectrical energy sources are designed to be charged to a significantdegree by an external power source. This is most typically done viain-ground charging of the stored electrical energy sources by externalpower, although could be accomplished in the future by wireless chargingwhile the aircraft is in flight. Alternately, the depleted storedelectrical energy sources are swapped with ones that were previouslycharged by an external power source.

In general, it may be understood in what follows that “hybrid” or“hybrid electric” powertrain or aircraft refers to the entire class ofpowertrain or aircraft respectively that integrate and/or combine one ormore stored electrical energy sources with one or more generatedelectrical energy sources. Hybrid-to-electric then is a subset of thesewhereby the one or more generated electrical energy sources is optional.Meanwhile, “electric” powertrain or aircraft refers to powertrain oraircraft that are powered by one or more stored electrical energysources, with no provision for generated electrical energy sourceswhatsoever.

In a conventional aircraft, one of primary functions of an enginecontroller is to regulate a flow of fuel to a propulsion engine in orderto produce suitable thrust. A typical aircraft engine controller,however, may not be applicable or otherwise useful to control anelectromotive power flow in a hybrid electric powertrain utilized by ahybrid electric aircraft as a source of propulsion. In some instances, apowertrain may be controlled, at least in part, on a sub-system orcomponent level, such as via sampling a directional feedback from aparticular generated electrical energy source and returning a commandsignal to the source to affect powertrain's performance in some manner,such as via leveraging generated power output, for example. At times,however, this or like approaches may be less dynamic, such as in termsof a suitable and/or desired response by a hybrid electric powertrain toparticular and/or changing load demands, for example, which may affectaircraft propulsion and/or overall powertrain performance. Accordingly,it may be desirable to develop one or more methods, systems, and/orapparatuses that may more effectively and/or more efficiently implementa system controller for a hybrid electric powertrain utilized by ahybrid electric aircraft as a source of propulsion.

For example, in some instances, one or more optimizations and/orimprovements may include implementing and/or utilizing a feedback loopor like process outside of an internal control loop of a particulargenerated electrical energy source, which may facilitate and/or supportmore effective and/or more efficient powertrain performance and/orcontrol. At times, one or more optimizations and/or improvements mayinclude, for example, more effectively and/or more efficientlyimplementing a “power split,” such as to facilitate and/or supportparticular power demands. In this context, “power split” refers to aproportion of electrical power delivery between a stored electricalenergy source (e.g., a battery, supercapacitor, etc.) and a generatedelectrical energy source (e.g., an electrical generator, fuel cells,etc.).

Referring now to FIG. 1, which is a schematic diagram illustratingfeatures of a plug-in series hybrid-to-electric powertrain, with anexample operating environment 100 capable of facilitating and/or supportone or more processes and/or operations for a system controller, such asan example left system controller unit (L SCU) illustrated generally at101. In some instances, system controller 101 may be capable ofcontrolling an operation of a powertrain, such as a plug-in serieshybrid-to-electric powertrain 102. The plug-in series hybrid-to-electricpowertrain 102 may, for example, be employed, in whole or in part, as asource of propulsive power and secondary electricals for ahybrid-to-electric electric aircraft. Thus, as illustrated, according toan implementation, powertrain 102 may comprise, for example, a number ofelements or components capable of generating, receiving, conditioning,and/or distributing electrical power from one or more electrical energysources, such as to drive or operate one or more particular electricmachine(s) that provide mechanical power for an associated propulsionsystem(s). As seen in this example, a particular electric machine maycomprise, for example, an electric motor, referenced at 10, that mayprovide mechanical power for an associated propeller, ducted fan, etc.(not shown). It should be noted that even though a certain number orelements or components of powertrain 102 are illustrated herein, anynumber of suitable elements or components may be implemented tofacilitate and/or support one or more operations and/or techniquesassociated with example operating environment 100.

In addition, it should be appreciated that even though two powertrainsare illustrated herein, such as for ease of discussion, any suitablenumber of powertrains may be associated with example operatingenvironment 100. The two plug-in series hybrid-to-electric powertrainshown, for example, mirror each other and comprise the same or similarelements or components operatively and/or communicatively coupled totheir own system controller unit 101, such as in the same or similarmanner. The mirrored powertrains improve reliability, to address and/ormitigate a risk of failure via redundancy, or the like. As a way ofillustration, a hybrid-to-electric electric aircraft may comprise, forexample, of the two series hybrid-to-electric powertrains shown andthese may be positioned on the right and left sides of the aircraft,such as to respectively power two electric motors in the same or similarmanner. In this example, while the left system controller unit 101 (LSCU) controls the left powertrain, a second right system control unit(not shown), would control the right powertrain. Alternately, a singlesystem control unit could be used control operations of the twopowertrains, such as in the same and/or similar manner. Also, eventhough system controller 101 is illustrated schematically in connectionwith a single communication bus, any suitable number of communicationbuses, redundant or otherwise, may be implemented herein, such as tofacilitate and/or support one or more operations and/or techniquesassociated with example operating environment 100.

In an implementation of a plug-in series hybrid-to-electric powertrain102 may comprise, for example, optional generated electrical energysources referenced as 103. In the implementation shown, the optionalgenerated energy source may comprise, for example, one or morecombustion engines 105 connected to generators 103, or one or more fuelcell 105 connected to voltage regulators 103. Generated electricalenergy sources are generally known and need not be described herein ingreater detail. As also seen, the optional generated electric energysource may be connected to controllers, referenced respectively for oneof the sources as the left generator control unit 106 (L GCU).Controller 106 may, for example, be capable of controlling operations ofoptional components 105 and 103, by monitoring one or more applicableparameters (e.g., speed, voltage, switching frequency, torque, coolanttemperatures, etc.) and/or communicating appropriate commands. Theseand/or other controllers discussed herein may, for example, beimplemented via ay suitable technology, such as programmable integratedcircuits, logic chips, control circuitry, etc. capable of facilitatingand/or supporting one or more operations and/or techniques associatedwith example operating environment 100.

According to an implementation, as illustrated via a power flow path at107, optional generated electrical energy source 105 may, for example,be electrically coupled to propulsion power panel 108. As also seen, astored electrical energy source 109 may also be electrically coupled orpropulsion power panel 108, such as via power flow path 110, forexample. In this particular implementation, a stored electrical energysource may comprise, for example, a battery 109, which may be in theform of a rechargeable battery pack. Here, battery 109 may comprise, forexample, its own controller, such as illustrated via a batterymanagement unit (BMU) 110 so as to control flow of electric power topropulsion power panel 108.

The stored electrical energy source 109 may be designed to be rechargedby external power sources, either by in-situ charging from an externalsource 127 via energy flow path 128, or by swapping source 109 with onethat was recharged to a greater degree by an external power source. Inaddition, the stored electrical energy source 109 may be recharged byregenerative braking using the propulsion electric motor 111, or by theoptional generated electrical energy source 105. Charging of the storedelectrical energy source 109 is controlled by system controlled 101working in concert with 110.

In some instances, propulsion power panel 108 may comprise, for example,an electrical sub-system or element having a matrix of electricalswitches with associated conductive paths so as to route electric powerfrom one or more applicable inputs to one or more applicable outputs. Inthe example shown, the power panel comprises electrical switches orcontactors 113, a high-voltage DC bus 114 (L HVDC bus), AC to DCconverters 115, DC to DC converters 116 and DC to AC inverters 117,collectively referred to as the Left Propulsion Motor controllers (LPMC). The converters and inverters are for the purpose of changingdirect current (DC) into alternating current (AC, DC to AC inverters),changing AC to DC (AC to DC converters), or for changing the voltagelevels of DC current (DC to DC converters). The converters and invertersshown may be implemented in any suitable manner, such as having suitablecomputing and/or processing resources (e.g., programmable chips,circuitry, memory, etc.) for example, to facilitate and/or supportappropriate control process and/or more intelligent inverter operation.

Thus, as illustrated, power panel 108 may comprise a controller,referenced at 112 left propulsion power panel controller (LP3 Cont.),which may be capable of implementing a particular switchingconfiguration of power panel 108, such as responsive to an appropriatecommand by system controller 101, for example. In some instances, aparticular switching configuration may, for example, be implemented byturning on and/or off one or more electrical switches (and/or associatedconductive paths) of power panel 108. For example, responsive to acommand by system controller 101, controller 112 may implement aparticular switching configuration of power panel 108 via routingelectric power from optional generated electric energy source 105 toelectric motor 111, while isolating stored electric energy source 109,just to illustrate one possible implementation. In some instances,controller 112 may also be capable of detecting operating parameters,conditions, faults, etc., of electrical switches, conductive paths,converters, etc. of power panel 108.

As further referenced vi a power flow path at 119, in an implementation,electric power from power panel 108 may, for example, be routed and/ordelivered, as appropriate, to electric motor 111, suitable operation ofwhich may be controlled by a motor controller 120, the Left MotorControls/Protection. As was indicated, electric motor 111 may, forexample, convert electric power into mechanical energy, such as tofacilitate and/or support appropriate thrust for a hybrid-to-electricelectric aircraft. Thus, electric motor 111 may be mechanically coupledto a suitable propulsor, such as a ducted fan, propeller, etc., forexample, capable of generating such thrust. Depending on the specificimplementation, motor controller 120 may comprise, for example, astand-alone unit communicatively coupled to motor 111, such as via alink 121, though claimed subject matter is not so limited. For example,in some instances, motor controller 120 may be part of electric motor111 (e.g., build-in, etc.). Motor controller 120 may, for example, becapable of controlling speed and/or torque of electric motor 111,communicating one or more operating parameters of electric motor 106 tosystem controller 101, determining health of electric motor 111, or thelike. In some instances, motor controller 120 may comprise and/or beassociated with inverters 117.

Also shown is an implementation of the secondary electrical system forthe hybrid-to-electric electric aircraft, indicated generally by thearrow 104. In the example shown, the secondary electrical system maydraw electric power at low voltage from the series hybrid-to-electricpowertrain 102, a low voltage stored electrical energy source 121 (LVBattery), such as the battery pack shown, and/or an external powersource 122 (Ext Pwr), typically engaged when the aircraft is stationaryon the ground. The power is in form of both, low voltage AC and lowvoltage DC. Low voltage AC is sourced from the DC to AC converters 115and/or external power 122. Low voltage DC is sourced from the DC to DCconverters 116, and/or the low-voltage battery 121, and/or externalpower 122. The power is then delivered to remote power distributionunits 124 (RPDU) via power flow paths 123, which condition the power forthe range of secondary loads on the aircraft. Power may also bedelivered to a starter 126 (S) that has the purpose of initiatingoperation of the optional generated electrical energy source 105.

As described extensively in U.S. patent application Ser. No. 16/107,821titled “System Controller for Series Hybrid Powertrain,” the entiredisclosure of which is hereby incorporated by reference, in operativeuse, system controller 101 may interface with a pilot cockpit, aircraftmanagement system, and/or one or more elements or components ofpowertrain 102 or secondary electrical system 104, such as via one ormore appropriate communications. For example, system controller 101 mayreceive a signal indicative of a particular input from these or likesystems, elements or components, and may perform one or moredeterminations and/or computations, such as based, at least in part, onthe input. The system controller 101 may compute one or more values soas to achieve a desired proportion of power delivery between storedelectrical energy source 109 and optional generated electrical energysource 105. System controller 101 may also compute one or more values toachieve a desired amount of power consumption by electric motor 111, forexample. In addition, system controller 101 may, for example, make oneor more determinations with respect to health of one or more elements orcomponents of powertrain 102 or the secondary electrical system 104and/or their operating capability. For instance, in case of failures ofcomponents in the left or right plug-in series hybrid-to-electricpowertrain, the System controller may determine that the setting of theswitch 118 should be adjusted to enable electrical power to flow acrossthe two powertrains to compensate optimally for these failures.

Control of Permanent Magnet Generators for Hybrid Powertrain

In one embodiment, the hybrid electric powertrain with a generationsource utilizes a wound-field synchronous generator that is fed to apassive diode rectifier to produce DC voltage. This DC voltage isconnected in parallel with a stored electrical energy source to providepower to a propulsion electric motor. The generator output voltage andcurrent are regulated to control the proportion of power delivered bythe generator relative to the stored electrical energy source to theelectric motor.

In an alternate implementation, a permanent magnet (PM) generator isutilized with an active rectifier to convert the AC output to DC. ThisDC voltage is again connected in parallel with a stored electricalenergy source to provide power to the propulsion electric motor. In anembodiment, the proportion of power delivered by the PM generatorrelative to the stored electrical energy source connected in parallel iscontrolled by means of a control process to regulate the output currentof the PM generator's active rectifier. The control process achievesthis current regulation by controlling the shaft speed of the PMgenerator or by controlling the switching modes of the active rectifier,or a combination of the two. The preferred method is by controlling theswitching modes of the active rectifier while maintaining the shaft ofthe PM generator at constant speed. Control of the shaft speed of the PMgenerator and/or the switching modes of the active rectifier can be doneby any conventional means.

It is well known that in a circuit with two parallel voltage sourcesserving a load, rectified generator and stored electrical energy sourcein our embodiment, the source with the higher voltage will delivergreater power to the load. Since the two sources are in parallel, theactual voltage on the shared bus will be the same, therefore, thedifferential amount of current flowing from each voltage source is theonly feedback available to control the proportion of power delivered byeach.

This approach has the additional benefit of enabling a seamlesstransition between physical, encoder- or resolver-based, and sensor-lessPM generator control in the event of encoder failure, improving thereliability of the hybrid powertrain. Rotor position information forcontrolling the flux and torque of a PM motor or generator is determinedtypically using a physical position encoder or a resolver. Sensor-lessalgorithms can also be applied to estimate the rotor position. Thesealgorithms use voltage and current sensing to estimate the rotor orstator flux vector, magnitude and position. In our embodiment, bothphysical and sensor-less methods are applied simultaneously where thephysical measurement is used primarily for flux and torque control. Thephysical measurement is also used to tune the sensor-less algorithm inreal-time to ensure very close alignment of rotor or stator flux vectorsdetermined by the two methods. In the event of any loss of communicationbetween the encoder or resolver and the controller, or any loss ofsignal integrity, the control software is designed to switch to thesensor-less algorithm. Given the estimate of the flux vector by thesensor-less algorithm is closely aligned to that determined by thephysical sensors, this transition from physical to sensor-less controlis seamless. Once the algorithm is transitioned to sensor-less mode, itcan continue in that mode for the remainder of the mission.

Power Electronics Building Block-Based Architecture for Propulsion PowerPanels

In an embodiment, the propulsion power panels (also referred to as a“Power Center”), of the hybrid electric powertrain are architected tosupport modular Power Electronics Building Blocks (PEBBs) for thetransfer of energy from sources to loads in a reusable, economical andefficient fashion, including appropriate DC and AC power conversion.Further, the Power Center to PEBB module interface is designedspecifically for high power, limited access applications such as thehybrid or electric aircraft powertrain where space and weight are bothat a premium. This is accomplished through deliberate design of theelectrical, mechanical, and coolant interfaces between the Power Centerand the PEBBs. In particular, while the Power Center carries full burdenof meeting the integration requirements with the aircraft andpowertrain, the interfaces with the PEBB is simplified to the minimumnumber of connections, made on the back of the module in the process ofmechanically linking the module to the Power Center. By this means,connectivity to electrical power, control, and thermal managementsystems is achieved via blind, secure connections that mate as the PEBBis joined with the panel.

As specific example of a PEBB, consider a series hybrid powertrain asdepicted in FIG. 1 in which both the generator 103 and electric motor111 are permanent magnet (PM) machines, with each PM generator rated at250 kW and each electric motor rated at 650 kW. An implementation of anAC-DC PEBB for this powertrain would be rated at 250 kW and designed toactively rectify power from a PM generator while controlling thedelivered voltage. In such an implementation, each generator would bedriven by one AC-DC PEBBs, and each electric motor would be driven bythree DC-AC PEBBs. As a result, the current demand for each machine willbe distributed roughly equally across the PEBBs, with some differentialdriven by dissimilar reactive power demands. The AC-DC PEBBs may bedesigned with additional thermal margins to allow higher frequencyoperation of the generator in situations where the generators is coupleddirectly to a high-speed turbine. In one example, the PEBB topologyconsists of a 6-switch 2-level converter with insulated-gate bipolartransistors (IGBT) and anti-parallel diodes. In another example, Silicon(Si) IGBTs and Silicon Carbide (SiC) diodes or SiC Metal OxideSemiconductor Field Effect Transistors (MOSFET) can also be used.Alternate implementations may include multi-level topologies with Si orSiC switches.

According to an embodiment, the PEBBs include a control platformconsisting of software and/or firmware and in which are implementedcontrol algorithms. In one example, the control algorithms are based onfield-oriented current control or torque control with feedback ofAC-side currents, DC voltage and position information of the PMmachines. In an another implementation, the control algorithm mayleverage algorithms including direct torque or flux control. The PEBBsare commanded by a propulsion power panel controller describedpreviously that runs outer control loops like voltage or speed controland generates current or torque commands. Fast protection against DCshort-circuit, over-current, over-voltage, over-temperature is builtinto the PEBB. Protection across PEBBs is coordinated by the propulsionpower panel controller which utilizes the modular nature of the systemto enhance overall system reliability and safety as will be discussedfurther herein.

FIG. 2 is a schematic of an embodiment of the Power Center with thePEBB-based hybrid power panel architecture, while FIG. 3 is anillustration of a Power Center physical implementation with modulesinstalled. In addition to the features described previously, the PowerCenter architecture (ref. FIG. 2) includes centralized controls,protection, communications and health monitoring 101. The architectureallows for the summing of the output power 102 of the DC-AC PEBBs 103.The architecture also allows bi-directional power flow 104 such thatregenerative power from the generator is supplied to charge thebatteries via the AC-DC PEBB 105. This feature includes a means tocontain regenerative power in the event the path to the batteries is notavailable. The architecture includes DC-to-DC converters 106 to supplylow-voltage power to the secondary electrical system 107, and alsoincludes additional DC-to-DC converters 108 for scenarios where controlof the high-voltage batteries 109 is required. Thermal management iscentralized, such that a single coolant flow 110 supports all componentsof the power panel. Similarly, Power Distribution Functions 112 such asthe Bus, Contactors and Backplane, and DC Bus protection 111 iscentralized.

FIG. 8 is a schematic showing the PEB 108 interfaces with the powercenter back plate 101, including the cooling fluid manifold 103 withfluid flowing into the PEBB 104 and return 105 through a singlequick-connect interface. Similarly, electrical power connections aremade with 106 and 107, along with control 109. In addition to theconnection points for services, the PEBB is mechanically anchored to theback plate 102.

Several approaches to control the power split from the generated versusstored electrical energy sources are illustrated in FIG. 2: an AC-DCPEBB 105 to passively rectify power from a Wound-field generator andleveraging the generator control unit (GCU) to control the requiredvoltage, an AC-DC PEBB to actively rectify power from a PM generator andcontrol the generated voltage level, and (C) HVDC DC-DC 108 convertorsto control the voltage of the stored electrical energy sources.

An example integration of the PEBBs described above is depicted in FIG.3, which shows a propulsion power panel 109 of the series hybridpowertrain wherein the three removable DC-AC PEBB modules 101 and theone AC-DC PEBB module 102 are mounted on an interconnecting backplane109. The PEBBs are designed for direct electrical integration to thepropulsion power panel through the backplane in a plug-and-playconfiguration. The power panel includes connections 103 to a generatedpower source, a stored energy source 104 and outputs to the electricpropulsion motor 105. The power panel also includes connections to thesecondary electrical system 106 and DC-to-DC converters 107 to conditionpower for delivery to this system. The PEBBs are architected for thecooling medium to be supplied to the PEBBs without need forindividualized plumbing as will be further described herein. As aresult, the power panel, when utilizing a single fluid, single loopthermal control system, requires just a single pair of fittings forcoolant inlet and outlet 108 from the ship's system. In case of adual-loop, dual-fluid system, described further herein, there would be asecond set of cooling fluid connectors to the backplane.

Novel Inverter Topologies for Hybrid Electric Powertrain

In a hybrid powertrain, power flow from the generator and to theelectric motor is controlled by DC-to-AC and/or AC-to-DC powerelectronic converters. Typical voltage levels for aircraft on the DCside of these converters are 270V or +/−270V. Given the high powerlevels required of the generators and electric motors, ranging in the100s of kW, the electric machines and power electronics (or PEBB asdescribed previously) must be be designed for high currents. Forexample, a 250 kW PEBB at 300Vac_rms output will need to have a currentrating greater than 500 A. These high currents require cables with largecross-section to between the PEBB, the electrical machines and otherpower sources, driving a significant increase in the weight of thesystem.

Meanwhile, the AC fundamental frequency of power-dense direct-driveand/or high pole-count electric machines often used on hybrid electricaircraft can exceed 1 kHz. This necessitates semiconductor switches ofhigh switching frequency to minimize torque ripple and machine losses,leading to high semiconductor losses in the PEBBs. For example, a 250kW, 300V, 3-phase 6-switch 2-level (2L) converter with Si IGBTs and SiCSchottky diodes is about 96% efficient at 20 kHz switching frequency. Inorder to keep losses low, voltages on both DC and AC sides of theconverters need to be raised. The 250 kW converter designed at 1 kV ACoutput and operating from 1.5 kVdc bus will have a current rating lessthan 200 A. As a result, the prior 2L topology would need to be designedto accommodate higher voltage devices. However, this leads to switchinglosses that are comparable or even greater than prior given highervoltage switches have higher switching losses.

This set of problems can be addressed by using multi-level topologiesbuilt with low-voltage semiconductor switches that enable lowerswitching frequency but achieve high power quality. Efficiency in theorder of 98.5% is possible with Si devices and 99% with SiC devices or ahybrid comprised of Si and SiC devices. In addition, the multi-levelconverter produces lower dv/dt at the converter AC terminal that whichhas the additional benefit of lowering EMI and insulation stress oncables and electrical machine windings.

In an embodiment of this novel concept, the PEBB for either inverter orrectifier operation is built with a 3-level (3L) or greater topology. Anexample PEBB configuration can use 3L neutral-point clamped (NPC)topology that produces voltage levels of +Vdc, 0, −Vdc at the ACterminal. Both active and passive clamping topologies could beimplemented. Other options are 3L neutral-point piloted (NPP) topologyusing series connected devices and AC-switches between the DC mid-pointand AC terminals. Alternately, a different class of multi-levelconverter called modular multi-level converter (MMC) can be designedwhere the PEBB is a sub-module of the MMC topology.

In an embodiment, these topologies enable the voltage rating ofindividual semiconductor switches to be significantly reduced. Forexample, a 2L topology at 1.5 kV DC bus will require a switch withgreater than 2 kV. A 3L topology for the same DC bus voltage can bebuilt with 1200V devices, and a 5L topology with 600V devices. The useof low voltage devices, accompanied with lower switching frequencyreduces semiconductor losses, improves power quality and reduces dv/dt.This translates to a much lighter powertrain, with significant benefitfor hybrid electric aircraft.

DC-to-DC Converter for Hybrid Electric Powertrain

In a hybrid electric aircraft, the power to drive the propulsionelectric motors is generated and delivered at as high voltage as isfeasible at altitude to minimize losses and system weight. This isaccomplished by means of a high-voltage propulsion electrical system.Meanwhile, a low-voltage secondary electrical system provides powers toa range of auxiliary loads such as avionics, cabin pressure, de-icing,landing gear etc. For example, while the propulsion electrical systemoperates at +/−270Vdc, standard aircraft electrical systems operate atvoltages as low as 28Vdc and provide power for the majority of aircraftelectrical equipment including avionics, lights, autopilot servos,landing gear actuation etc. The propulsion electrical system is notsusceptible to high-frequency electromagnetic interference (EMI),however, the auxiliary loads, and in particular the avionics andcontrols, are very much impacted by EMI requiring adherence to stringentstandards.

In an embodiment, the secondary DC voltage, 28Vdc for example, isderived from the primary DC voltage, +/−270Vdc for example, by step-downDC-to-DC converters that include EMI filtering to prevent anyinterference from the propulsion electrical system to the secondaryelectrical system. Since the power required by the secondary electricalsystem is a small fraction of that on the propulsion electrical systemand the electromagnetic energy content is orders of magnitude smaller,the filters deployed are correspondingly smaller in size and weight. Asnoted previously, the distribution of HVDC is packaged within propulsionpower panels with power interfaces to the generated and storedelectrical energy sources and the propulsion electric motors. Thelow-voltage secondary distribution derived from the HVDC via theDC-to-DC converter feeds the secondary electrical system. Theimplementation of EMI filtering on the secondary electrical system isdone via passive components, e.g., common-mode and differential modeinductors, capacitors, etc., or by deploying widely understood activefiltering techniques.

Inverter Topology for In-Ground Charging a Hybrid or Electric Powertrain

In hybrid or electric aircraft, a significant fraction of the energycontained within the stored electrical energy sources is derived bycharging these when the aircraft is on the ground, e.g., from the grid.Some energy can be regenerated while in the flight, but the primarymeans of replenishing the stored electrical energy sources on theaircraft is via a suitable charger on the ground.

In an innovative embodiment shown in FIG. 4, the charging on the groundis achieved via power electronics converters designed for dual-use toreduce cost and weight: (i) as an inverter to drive the propulsionmotor, and (ii) as a converter for charging the stored electrical energysource on the ground. In FIG. 4, the DC-to-AC power electronicsconverter 101 is connected to a set of contactors 102 on the AC side viaAC cables 103. One set of 3-phase AC cables 104 is connected to thepropulsion electrical motor 105. When the propulsion electrical motor isoperating, the contactors connect the converter to the motor to transferenergy from the generated and/or stored electrical energy sources topower the aircraft.

Charging is accomplished by an in-ground system 100 that connects to thecontactor 102 via a set of 3-phase AC cables 106, either directly or viaan intermediate interface. These cables 106 are in turn connected to anin-ground transformer 107 to provide the required matching voltage andisolation, while the primary side of the transformer is connected to the3-phase in-ground power grid 108. When charging, the contactors for thepropulsion electrical motor 105 are disconnected, and the contactors forthe in-ground system 100 are connected, thereby enabling power flow fromthe AC side to the stored electric energy source appropriately routed bythe propulsion power panel 109.

The power electronics converter 101 in the charging mode of operation iscontrolled as a boost active rectifier, where the peak of the AC sidevoltage is lower than the minimum voltage of the stored electricalenergy source. The transformer 107 is designed with appropriate leakageinductance to act as the boost inductor. As a result, no additionalfiltering may be necessary within the aircraft to enable the chargingoperation.

Control Methods for Hybrid or Electric Powertrain

For a hybrid or electric powertrain with an inverter driving apropulsion electric motor, it is sometimes advantageous to minimize thetotal losses of the inverter and motor, rather than minimizing thelosses of the inverter and motor separately. The losses are a functionof several parameters, one of these being the switching frequency andthe switching instants of the inverter, which depends on thepulse-width-modulation (PWM) method employed. The harmonics in thevoltage waveform result in harmonics in the machine current, flux andtorque, thereby resulting in harmonic losses in the motor and torqueripple on the shaft. As the machine fundamental frequency increases, theswitching frequency also needs to be increased to maintain high powerquality. This results in increasing losses on the inverter. A lowerswitching frequency shifts some losses from the inverter to the motorwith higher torque ripple and vice-versa. The type of PWM method usedalso determines the common-mode voltage generated due to switching,which impacts EMI, bearing currents etc. and can be minimized as much aspossible.

An embodiment of our novel control process uses a PWM method withpre-computed pulse-patterns that are synchronous to the fundamentalvoltage waveform. First, a cost function is defined with the parameters:(i) total losses in the inverter and motor; (ii) total harmonicdistortion of the inverter voltage, which represents power quality;(iii) common mode voltage magnitude of the inverter voltage. Eachparameter is bound within certain limits based on the specificimplementation of the inverter and motor. Second, the cost function isminimized within these constraints by varying the pulse number and pulsepattern (width and location of the pulses) within a fundamental cycle ofthe voltage waveform, maintaining half-wave and quarter-wave symmetries.The computation of the pulse patterns is done over the entire operatingrange of the motor. A design of experiment (DOE) is conducted tominimize the number of computations and curve-fitting techniques areused to extrapolate the switching angles. Finally, a comprehensivelook-up table of switching angles corresponding to the pulse patterns isgenerated as a function of output voltage magnitude, speed and load ofthe motor.

The motor controller runs closed loop current control to generate avoltage reference for the inverter. It then uses this look-up table tocommand the specific switching states of the inverter based on thevoltage, current and fundamental frequency at that operating point.

Synchronized Operation Between Modular Inverters without ExternalFiltering

For a hybrid powertrain at low voltage, e.g., less than 1 kVdc, thepropulsion electric motor is often designed for high current. As anexample, a 500 kW, 300V (line-to-line rms) motor with a rated powerfactor of 0.8 will have a rated current of 1200 A. This may lead themachine to be built with multiple segments, each segment housing a groupof 3-phase windings. A machine with 3 segments has a current per phasegroup of 400 A, which is much easier to feed from an inverter. Thisdesign requires 3 modular inverters to be built and configured to driveeach phase group. Such an operation of parallel inverters has theadditional benefit of reducing the flux and torque ripple, while alsominimizing voltage stresses between the windings of different phasegroups.

In our novel embodiment, the relative switching instances between theinverters is tuned to minimize flux and torque ripples. Interleaving theswitching between the different phase groups and between the phases ineach group results in effective increase of the ripple frequency of themachine flux and torque. FIG. 5 demonstrates this for an example ofcarrier waveforms with 3 phase groups. The carriers corresponding togroup 1 for the 3 phases are A1, B1, C1 (120° apart at switchingfrequency level). Group 2 phases are shifted by 120° from Group 1 andGroup 3 phases are shifted by 120° from Group 2. So, A1-B3-C2 arerepresented by one carrier waveform, A2-B1-C3 by another carrierwaveform and A3-B2-C1 by the 3^(rd) carrier waveform. The carriers canbe either synchronous or asynchronous to the fundamental. This resultsin an effective improvement of the flux and torque ripple by 3 times thecarrier frequency and eliminates the need for external filtering.

In motor designs where coils from different phase groups share a slot ina segment, this type of interleaving will produce high differentialvoltage between the coils and will need suitable insulation to ensurelong-term reliability. In such designs, the phase shifting between phasegroups is avoided, however, the phase shifting between the phases isstill effective.

Novel Cooling Systems and Methods for Hybrid and Electric Powertrain

Powertrain architectures for aircraft typically require active coolingof significant components including motors, generators, inverters, andin some cases wiring. In many cases, maximum sustained power output isdirectly related to the ability to effectively cool the electricalcomponents. This challenge is significantly amplified when thepowertrain is integrated within an aircraft where both space and weightare at a premium, and a heat exchanger exposed to free stream airflowwill result in an aircraft drag penalty. Further, while liquid coolingmay enable a more compact, lower weight component design, the liquidcooling system itself then requires plumbing, fluid, pumps and power forpumping all of which add weight and volume. Various embodiments suitablefor cooling such a powertrain and/or PM generator are discussed herein.At the system level, these cooling architectures are suited forapplication go the modular PEBB and Power Center Backplate architecture,wherein each attached module is plugged into system level coolant flowon connection to Power Center.

Single-loop steady-state cooling of PEBBs: In one embodiment,steady-state cooling of PEBBs is achieved by introducing a closed loopcoolant system containing a dielectric fluid (DF), for example 3MHFE-7500. This system consists of a central fluid reservoir, one or morecoolant pumps, a filtering system, and a fluid-distribution manifoldwhich distributes the flow evenly into all the PEBBs in the power panel.Within each panel, the pumped DF removes heat from heat sinks in eachindividual PEBBs, and then passes through an environmental HX to dumpthe heat prior to returning to the reservoir. In one embodiment, thecooling air for the HX is provided by the free stream flow. In anotherembodiment in which the cooling is directed at a generator, cooling airis siphoned from a duct connected to the generator turbine inlet scoop.

Multiple Cooling Loops: In another embodiment, two cooling loops areutilized. In one implementation, the previously described DF coolantloop dissipates heat from all the PEBBs that drive the propulsion motor;while the second loop utilizes a second coolant type appropriate to theoperating temperature and heat flux requirements. In on implementation,the second loop working fluid consists of an equal percentage ofethylene-glycol-water (EGW) and provides cooling to the other PEBBs suchas DC-DC converters, and active rectifier for the EPGS in the powerpanel. In such an embodiment, each loop is a complete system includingtwo reservoirs, one for each DF and EGW, with their respective pumps andfiltration systems. In one embodiment, the difference in operatingtemperatures of the coolant loops enable higher system efficiency. Inthis system a DF-EGW counter-flow HX exchanges heat from the outlet ofthe DF-cooled PEBBs to the inlet of the EGW-cooled PEBBs, and heatexchange to the environment is made with the EGW coolant loop and an airto EGW heat exchanger.

Single-loop Cooling of multiple components: According to anotherembodiment, the cooling system consists of a single loop of the motorand the central thermal system of the primary power panel. In thisembodiment, a single pump and a filter system drives the same DF throughthe PEBBs and the propulsion motor(s). In one implementation, withsufficient fluid volume, the reservoir is omitted to save weight. Inthis embodiment, the cold DF is distributed evenly through the inletPEBB-manifold, it is heated along the length of the PEBBs and iscollected in the outlet PEBB-manifold. As a continuation of the singlecooling loop, the same DF is now evenly distributed using amotor-manifold around the circumference of the propulsion motor. In thisimplementation, with a dielectric fluid as coolant, the windings areimmersion-cooled. In another implementation, the motor coolant isprovided by pumped two-phase cooling along the back-iron channels of thestator. In this implementation the final temperature of the DF issignificantly above ambient presenting a challenge to minimize theweight and space of the environmental HX. In one implementation, thiscan be addressed with a dual-sided HX, in which, the first side iscooled from the vapor-compression air-conditioning system, and the otherside from ram-air provided by free stream air flow.

Phase-change cooling, Background: Phase change immersion-cooling, and inparticular boiling, has emerged as the primary choice for extremely-highheat flux dissipation from high-efficiency silicon-carbide (SiC) powerelectronics. A key limiting boiling phenomenon that prevents safeoperation of power switching devices at full-load is the critical heatflux (CHF): a cataclysmic failure point where the surface is completelyblanketed by vapor and the efficacy of surface heat transport isthrottled by several orders of magnitude, beyond which the surfaceexperiences severe burnout.

Theoretical and experimental research has been conducted to study thekey passive methods that could potentially delay the onset of CHF.Surface wettability (contact angle) and texturing has been shown toinfluence a number of aspects of boiling heat transfer, mainly the CHF,surface superheat, and bubble incipience, departure and frequencycharacteristics. In general, heat transfer coefficients (HTC) are higherfor less-wetting surfaces (surfaces with contact angle exceeding 90degrees), as a result of low superheat at bubble incipience and highbubble nucleation density; conversely, CHF is higher for more-wettingsurfaces (surfaces with contact angle below 90 degrees), due toeffective rewetting of the surface after bubble departure. As it isextensively pointed out in the literature, textured super-hydrophilic(more-wetting) surfaces have shown significant enhancement in CHFthrough capillary wicking, albeit with moderate HTC. On the other hand,super-hydrophobic (less-wetting) surfaces reduce the CHF and transitionto film boiling with high HTC. The two possible wetting states ontextured superhydrophobic surfaces during nucleate boiling are: theCassie-Baxter state, where the liquid rests on top of themicro-/nano-structures and vapor is trapped in the rough solid-liquidinterface regions leading to low frequency in bubble departure (˜0.2Hz); and the Wenzel state which limits vapor spreading and maintainsnucleate boiling to a much higher CHF than Cassie-Baxter state at higherbubble departure frequencies (˜31 Hz). The trade-off between twodesirable thermal performance traits (high CHF and high HTC) as afunction of surface wettability is the driving motivation behind thisinvention.

Improved multi-phase heat transport using a laser etched biphilicsurface incorporating copper nanowires: According to an embodiment, thefavorable boiling heat transport characteristics of hydrophobicitywithout simultaneous reduction in CHF are obtained utilizing asymbiotically-textured surface (or a biphilic surface) which comprisesof hydrophobic regions that act as nucleation sites on a uniformhydrophilic surface. This renders a textured surface, either withnanostructures or microstructures, that shows concomitant enhancement inHTC and CHF compared to conventional flat surfaces and uniformhydrophilic surfaces. In this embodiment the textured surface issynthesized in two steps: laser etching to produce a carpet ofmicro-structured pillars on a flat surface of the heated switchingdevice (act as super-hydrophilic); and chemical etching of coppernanowires (act as super-hydrophobic) on the top face of the pillars.

The innovation of applying phase change immersion cooling system usingbiphilic textured surfaces can significantly improve the thermalperformance by increasing the frequency of bubble ebullition andallowing for periodic renewal of colder liquid to replace the departingbubbles. The CHF is increased dramatically which allows for bulk liquidtemperature operation closer to the saturation temperature (boilingpoint) of the fluid. This reduces the thermal load on the centralaircraft thermal management system that exchanges heat between air andthe PEBB thermal system.

Self-Cavitating Multi-Jet Impingement Boiling for Surfaces with VeryHigh Heat Flux:

Background: As the trend of high-power electronics and concomitantminiaturization escalates to faster switching devices and rising demandson control, aerospace/aviation-grade inverters continue to become morecompact in response to size limitations, reliability requirements andweight restrictions. The result is an increasing surface heat flux atthe power module level; the transistor packages of a SiC(silicon-carbide) IGBT (insulated gate bipolar transistor) moduleapproach 0.3-0.4 kW/cm′, while GaN (gallium-nitride) wide bandgaptransistor electronics encounter intense power densities of 1 kW/cm′. Inaddition to the inability to provide heat removal capacity of suchmagnitudes, the present cooling solutions suffer from two majordrawbacks: a thermal-interface-material (TIM) between the powersemiconductors and the heat sink that contributes massively to the netthermal resistance; and the presence of a temperature gradient along themodule surface in the direction of fluid flow, which increases with thepower capability of the module. Therefore, thermal management of thehigh-power-density inverters requires state-of-the-art coolingstrategies capable of overcoming these pitfalls, and continuouslydissipating high heat fluxes (˜0.5-1 kW/cm′) while maintaining theswitching devices below their maximum allowable junction temperature,thereby optimizing the package for minimum volume, weight and pumpingpower.

Superposition of phase-change heat transfer (pool boiling in this case)with high convection heat transfer coefficients achieved by submergedjet impingement, wherein the liquid jet issues from a nozzle onto asurface surrounded by a fluid medium with the same environment as thejet, can enhance heat removal capability while also providingtemperature uniformity. The sweeping of vapor bubbles nucleating fromthe heated surface by the impinging liquid jet increases the surfaceheat flux due to the latent heat of vaporization. The heat transferregimes observed in phase change jet impingement as the surface heatflux rises include: a single-phase regime before boiling incipience, apartial-boiling regime, and a fully-developed nucleate boiling regime,followed by critical heat flux (CHF) beyond which the surfaceexperiences burnout. During the transition from single-phase regime tofully-developed nucleate boiling regime in the presence of a dielectricfluid, the heated surface of the power module undergoes a temperatureovershoot, which is essentially the difference in the surface superheat(difference between the surface temperature and the bulk fluidtemperature) attained before and after boiling incipience. The surfacecan encounter temperatures from 25° C.-40° C. above the boiling point ofthe fluid during temperature overshoot; this is cardinal intemperature-sensitive applications such as power electronics becausefailure to initiate boiling can cause severe damage to the power module.

Overshoot prevention with higher heat flux through modified jet nozzles:In one embodiment a geometrical modification to the jet nozzle thateliminates the temperature overshoot of the heated surface. A“self-cavitating” nozzle is described wherein a concentric collar isattached at the tip of the circular jet nozzle. The collar provides anexpansion region for the jet flow at the exit of the nozzle that createsa pressure drop, which in turn results in the generation of a cloud ofcavitation bubbles that impinge on the heated surface. These impingingcavitation bubbles slide over the heated surface, thus providing theliquid-vapor interface essential for an early onset of boiling andelimination of temperature overshoot. In addition, the inherent flowoscillations produced by the cavitation bubbles enhance the surface heattransfer rate per unit coolant mass flux beyond that is currentlyachieved by jet impingement, with no additional pumping power.

In an embodiment, the cross-section of the cooling device containsmultiple self-cavitating jets impinging onto a pair of SiC powersemiconductors (IGBT and diode). The device contains an inlet manifoldwith channels that distribute flow evenly into each self-cavitatingnozzle, and a similar outlet manifold that collects the spent liquidthrough a pair of siphoning sections situated on either side of theself-cavitating nozzle. As cavitation occurs near the tip of the collarat a certain threshold jet Reynolds number and collar-to-nozzle spacing,the flow disturbances introduced by the cavitation bubbles periodicallyrenew the hydrodynamic and thermal boundary layers by pushing the vaporbubbles nucleating from the heated surface and directing them into thesiphoning sections of the fluid chamber. The temperatures of the fluidchamber and the jet are maintained several degrees below the boilingpoint of the fluid, and this allows rapid condensation of the vaporbubbles inside the pool within the siphoning sections of the chamber,thereby not allowing vapor bubbles to occlude the outlet manifold.

In this embodiment, localized surface heat transfer capabilities up to10 W/cm²-K are achievable with improved surface temperature uniformitythan the currently utilized single-phase and two-phase heat transfersolutions. Further, the cooling device is designed to particularly workwith dielectric fluids enabling switching devices to be completelyimmersed in the liquid chamber for a compact packaging ofpower-electronic-building-blocks (PEBBs). The direct contact ofswitching devices with a dielectric fluid means that even in the absenceof boiling heat transfer, the combination of self-cavitating bubbles andjet impingement would provide adequate cooling with heat transfercoefficients of the order of 0.5-2 W/cm²-K.

Since the flow rates for the nozzle, even at turbulent jet Reynoldsnumbers, are lower than the flow rates for orthodox forced convectioncooling solutions, the pumping power is remarkably small—this means thatthe weight and volume of the ancillary equipment such as pumps, flowmonitoring systems, fittings are also minimized.

Microchannel Heat Sink for Two-Phase Cooling, Background:

High-power SiC switching devices experience heat fluxes exceeding 1kW/cm², which must be dissipated while maintaining the device junctiontemperatures at levels safe for reliable operation. Current coolingsolutions are indirect and utilize a heat sink that is separated fromthe silicon die with heat spreaders inserted between. Large temperaturerises across this stack occur due to the parasitic thermal interface andspreading resistances between the switching device and the attached heatsink. Additionally, heterogeneous heating—specifically localized hotspotheating—can cause extreme temperature variations across device surfaces.These application trends necessitate the development of transformativecooling strategies, with coolant channels deployed directly on thesemiconductor device. While direct cooling allows for reduced thermal(conduction) resistances and eliminates contact resistances, there islittle material thickness between the heat-generating device and theheat sink available for heat-spreading; this exposes the heat sinkdirectly to heat fluxes generated from the device and entails higherheat transfer coefficients to maintain the low thermal resistance acrossthe heat sink. Local hotspots also lead to high local junctiontemperatures and large temperature gradients across the device.

Heat sinks containing deep, high-aspect-ratio microchannels provide highheat transfer coefficients and large area enhancement, which them anideal candidate for high-heat-flux applications. Single-phasemicrochannel heat sinks have been widely studied for power electronicscooling and the consensus is that the pressure drop along the length ofthe channels leads to large pumping power requirements at small channeldiameters and high flow rates.

Two-phase operation can enable reductions in size, weight and overallpumping power consumption when compared to single-phase systems. Phasechange evaporative cooling in traditional microchannel heat sinks hasbeen widely explored and found to improve surface temperature uniformityand heat dissipation efficacy relative to single-phase cooling. Atraditional microchannel heat sink contains a single inlet, an array ofmicrochannels spanning the entire device length, and a single outlet.Even with the advent of evaporative cooling designs, the maximum heatdissipation of these traditional microchannel heat sinks remains limitedby impractically large pressure drops as the channel dimensions decreaseand vapor volume fractions increase.

According to an embodiment depicted in FIG. 6, dimensions of the devicebeing cooled can be decoupled from the flow length by the introducingthe working fluid at multiple locations along the length of themicrochannels, resulting in multiple flow paths of decreased effectiveflow length. A multi-level, structured microchannel heat sink where theheated surface is discretized into banks of multiple heat sinks, eachwith its own dedicated inlet and outlet fed in parallel. The pressuredrop is significantly reduced at a given mass flux due to the decreasein channel flow length. The heat sink contains inlet and outlet headerswith parallel flow passages that span the width of the switching device.The flow impinges on the channel base, splits and travels along thechannel in both directions, and exits the channel through the plenumchamber.

In some instances, due to increased number of parallel flow paths inthis microchannel heat sink, flow maldistribution between channels,caused by uneven pressure drop within the manifold, can causesignificant performance reduction and temperature heterogeneity. Inorder to mitigate this, the manifold passages leading to the individualchannels increase in cross-sectional area and are located in the flowdirection such that each parallel microchannel encounters the samepressure drop.

In many power electronics cooling applications, non-uniform heatgeneration is common. This microchannel heat sink design limits thelateral temperature gradients on the surface of the switching device andensures localized cooling of hotspots depending on the spatial locationof the junction of the switching device. The banks of small-width andhigh-aspect-ratio microchannels reduce the overall pressure drop of thethermal system by decreasing the effective flow length of all parallelflow paths within the system.

Fail-Safe Cooling: An embodiment of the innovations described hereinrelates to an aircraft with multiple redundancies in the powertrainincluding a plurality of propulsors, each of which are driven by one ormore motors, a plurality of stored energy sources, for examplebatteries, and further may include one or more sources of generatedpower. In one embodiment, such a series-hybrid electric aircraft isconfigured with two channels—left and right—that each deliver power fromenergy sources to motor loads. There is a connection between the twosuch that if one side fails, then the other side can re-route power tosupport the deficiency. For example, if the left load motor fails, thenthe right motor can be driven beyond its typical operating point withadditional power coming from the left battery. In such a situation, ifthe motor is driven beyond its normal continuous operating point, itwill eventually overheat without additional cooling. A similar examplecan be considered with the power electronics that drive the motor. Ifmultiple inverters are used to drive a single motor and one of theinverters fails, then the other two can be operated at much higher powerlevels for a limited period of time in an effort to compensate.

In one embodiment in which a single loop, single fluid cooling systemfeeds a set of power electronics and electric machines in ahybrid-electric or purely electric powertrain architecture, the systemcontroller can redirect coolant from faulted components to healthycomponents. This redirection is made through actively controlled valvesin distribution channels or manifolds, and is made simultaneously withthe re-direction of power to the healthy components to mitigate theadditional thermal demands.

In a second embodiment in which there are multi-loop, multi-coolantsystems, as previously described, the redirection logic is specific toeach separate such cooling system.

The invention claimed is:
 1. A hybrid or electric powertrain apparatusfor an aircraft comprising: one or more control units; one or moremodular power convertor units communicatively coupled to at least one ofthe one or more control units; and a power panel communicatively coupledto at least one of the one or more control units, the power panel tocomprise: a plurality of electrical interfaces for connection to one ormore sources and one or more loads, the one or more loads comprising atleast one electric propulsion motor to provide thrust to the aircraft; aplurality of electrical and mechanical interfaces to enable the one ormore modular power converter units to be detachably affixed andelectrically connected to the power panel; and a plurality of switchesand associated conductive paths, configurable in response to commandsfrom the one or more control units, to route electrical power betweenthe one or more sources and the one or more loads connected to the powerpanel, and selectively condition electrical power routed between atleast one of the one or more sources and at least one of the one or moreloads through the one or more modular power converter units detachablyaffixed to the power panel, wherein: the power panel further comprises aplurality of no-drip coolant interfaces; at least a first modular powerconvertor unit of the one or more modular power convertor units to forma first cooling fluid manifold while one or more coolant interfaces onthe first modular power convertor unit are detachably affixed to the oneor more of the no-drip coolant interfaces; and the first cooling fluidmanifold to allow a cooling fluid to flow into the first modular powerconverter unit and return fluid to flow from the first modular powerconvertor unit.
 2. The apparatus of claim 1, wherein the one or moremodular power convertor units include conditioning circuitry to: convertAC power from the at least one of the one or more sources to provide DCpower to the at least one of the one or more loads; convert DC powerfrom the at least one of the one or more sources to provide an AC powerto the at least one of the one or more loads; convert high-voltage powerfrom the at least one of the one or more sources to provide low-voltagepower to the at least one of the one or more loads; or convertlow-voltage power from the at least one of the one or more sources toprovide low-voltage power to the at least one of the one or more loads,or a combination thereof.
 3. The apparatus of claim 1, and furthercomprising: a common modular mechanical interface to detachably affixthe one or more modular power convertor units to the power panel; and acommon electrical interface to detachably connect the one or moremodular power convertor units to the power panel.
 4. The apparatus ofclaim 1, wherein the power panel and at least a second modular powerconvertor unit of the one or more modular power converter units to forma second cooling fluid manifold while one or more coolant interfaces onthe second modular power converter units are detachably affixed to oneor more of the plurality of no-drip coolant interfaces, and wherein thefirst cooling fluid manifold and the second cooling fluid manifold areto allow the cooling fluid to flow from a central fluid reservoir. 5.The apparatus of claim 1, wherein the power panel comprises one or morecooling system loops on one or more cooling fluid manifolds operable inresponse to one or more commands from the one or more control units todirect flow of cooling units to the one or more cooling fluid manifolds.6. The apparatus of claim 1, wherein a state of the power panel isdefined, at least in part, by at least one electrical signal applied tocorresponding ones of the plurality of switches.
 7. The apparatus ofclaim 1, and wherein the power panel is configurable responsive to oneor more commands from the one or more control units to route electricalpower: from at least one stored electrical energy source to the at leastone electric propulsion motor, and to at least one secondary load; fromat least one generated energy source to the at least one electricpropulsion motor, to at least one secondary load, and to recharge atleast one stored electrical energy source; from a high-voltage powersource external to the aircraft to recharge at least one storedelectrical energy source; from a low-voltage power source external tothe aircraft to at least one secondary load; or from the at least oneelectric propulsion motor when regenerative braking to recharge at leastone stored electrical energy source, and to the at least one secondaryload, or a combination thereof.
 8. The apparatus of claim 1, and whereinthe power panel is configurable responsive to one or more commands fromthe one or more control units to route electrical power between a firsthybrid or electric powertrain and a second hybrid or electricpowertrain.
 9. A hybrid or electric powertrain apparatus for an aircraftcomprising: one or more control units; one or more modular powerconvertor units communicatively coupled to at least one of the one ormore control units; and a power panel communicatively coupled to atleast one of the one or more control units, the power panel to comprise:a plurality of electrical interfaces for connection to one or moresources and one or more loads, the one or more loads comprising at leastone electric propulsion motor to provide thrust to the aircraft; aplurality of electrical and mechanical interfaces to enable the one ormore modular power converter units to be detachably affixed andelectrically connected to the power panel; and a plurality of switchesand associated conductive paths, configurable in response to commandsfrom the one or more control units, to route electrical power betweenthe one or more sources and the one or more loads connected to the powerpanel, and selectively condition electrical power routed between atleast one of the one more sources and at least one of the one or moreloads through the one or more modular power converter units detachablyaffixed to the power panel, wherein the power panel is configurableresponsive to one or more commands from the one or more control units todeliver set proportions of power from at least one stored electricalenergy source and at least one generated electrical energy source to theat least one electric propulsion motor.
 10. The apparatus of claim 9,wherein the one or more control units determine the set proportions ofpower based, at least in part, on a calculated voltage setpoint valuefor at least one of the one or more sources.
 11. The apparatus of claim9, wherein the one or more control units determine the set proportionsof power based, at least in part, on one or more measurements ofresulting power delivered from the one or more sources to the at leastone electric propulsion motor.
 12. A method comprising: applying one ormore command signals to a power panel, wherein the power panel comprisesa plurality of electrical interfaces connected to one or more sourcesand one or more loads, the one or more loads comprising at least oneelectric propulsion motor to provide thrust to an aircraft; a pluralityof electrical and mechanical interfaces to detachably affix andelectrically connect to one or more modular power converter units;directing a cooling fluid through a first cooling fluid manifold into afirst modular power converter unit of the one or more modular powerconverter units; and directing a return fluid from the first modularpower converter unit through the first cooling fluid manifold, wherein:the first cooling fluid manifold formed by attachment of a coolantinterface of the first modular power converter unit of the one or moremodular power convertor units to a first coolant interface of the powerpanel; and application of the one or more command signals to the powerpanel configures a plurality of switches and associated conductive pathsto route electrical power between the one or more sources and the one ormore loads connected to the power panel, and selectively conditionelectrical power routed between at least one of the one more sources andat least one of the one or more loads through the one or more modularpower converter units.
 13. The method of claim 12, wherein selectivelyconditioning electrical power routed between at least one of the onemore sources and the at least one of the one or more loads through theone or more modular power converter units further comprises: convertingAC power from at least one of the one or more sources to provide DCpower to the at least one of the one or more loads; converting DC powerfrom the at least one of the one or more sources to provide an AC powerto the at least one of the one or more loads; converting high-voltagepower from the at least one of the one or more sources to providelow-voltage power to the at least one of the one or more loads; orconverting low-voltage power from the at least one of the one or moresources to provide low-voltage power to the at least one of the one ormore loads, or a combination thereof.
 14. The method of claim 12,wherein the cooling fluid flows from a central fluid reservoir, themethod further comprising: directing the cooling fluid through a secondcooling fluid manifold into a second modular power converter unit of theone or more modular power converter units; and directing a return fluidfrom the second modular power converter unit through the second coolingfluid manifold, wherein the second cooling fluid manifold is formed byattachment of a coolant interface of the second modular power converterunit of the one or more power convertor units to the first coolantinterface of the power panel.
 15. The method of claim 12, and furthercomprising: directing a flow of cooling fluid to one or more fluidmanifolds through one or more cooling system loops responsive to one ormore commands from one or more control units.
 16. A method comprising:applying one or more command signals to a power panel, wherein the powerpanel comprises a plurality of electrical interfaces connected to one ormore sources and one or more loads, the one or more loads comprising atleast one electric propulsion motor to provide thrust to an aircraft;and a plurality of electrical and mechanical interfaces to detachablyaffix and electrically connect to one or more modular power converterunits; and delivering set proportions of power from at least one storedelectrical energy source and at least one generated electrical energysource to the at least one electric propulsion motor responsive to theone or more command signals, wherein application of the one or morecommand signals to the power panel configures a plurality of switchesand associated conductive paths to route electrical power between theone or more sources and the one or more loads connected to the powerpanel, and selectively condition electrical power routed between atleast one of the one more sources and at least one of the one or moreloads through the one or more modular power converter units.
 17. Themethod of claim 16, and further comprising: determining the setproportions of power to be delivered based, at least in part, on acalculated voltage setpoint value for at least one of the one or moresources.
 18. The method of claim 16, and further comprising: determiningthe set proportions of power based, at least in part, on one or moremeasurements of resulting power delivered from the one or more sourcesto the at least one electric propulsion motor.